The teenager , named only as Alexander K, is accused of carrying out the horrific crimes at his family home in the city of Tambov in western Russia's Tambov Oblast region.
His father Victor, 43, his sister Victoria, 14, and his grandmother Vera, 67, were all found brutally murdered in their blood-soaked beds with multiple axe wounds.
Police say the boy's relationship with his family had become strained following the death of his mother from cancer three years ago and he did not get on with his father's new girlfriend.
However, cops claim the final straw appeared to be that the family had refused his request to borrow 200,000 RUB (£2,788) from them.
Neighbours said that Alexander appeared to have suffered from depression following the death of his mother. He had stopped spending time with his friends and had even reportedly joined a sect.
Police are continuing to question Alexander, who remains in custody. He is expected to be charged with murder. The police investigation continues.